A lithographic exposure apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic exposure apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic exposure apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Irrespective of the tool used, the substrate may be subjected to a variety of processes before the exposure process. For example, as indicated above, the substrate will generally be treated with resist before exposure. Also, prior to exposure, the substrate may be subjected to cleaning, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, priming, resist coating, soft bake processes, and measurement processes.
The substrate may also be subjected to a host of post-exposure processes, such as, for example, post exposure bake (PEB), development, hard bake, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, cleaning, and measurement processes. And, if several layers are required, which is usually the case, the entire procedure, or variants thereof, will have to be repeated for each new layer.
These pre- and post-exposure processes are typically performed by stations or modules designed for their respective purposes. The substrate is subjected to these processing modules, as well as the lithographic exposure apparatus, typically in a pre-defined sequence. In this arrangement, the substrates travel in a pre-specified processing path to get serviced by specific processing modules that can be tracked. The processing path can be monitored, recorded, controlled, and limited to specific paths.
As indicated in FIG. 1A, which schematically depicts a lithographic system 100, substrate track apparatus 104 interconnects lithographic exposure apparatus 102 with a host of pre-processing modules 104, 106 and post exposure processing modules 104, 108. The pre- and post-exposure processing modules 104, 106, 108 may be apparatus that are external and/or internal to the substrate track 104. To accommodate the transfer of substrates between these processing apparatus, the substrate track 104 may include interface sections and apparatus configured to transport the substrates to and from the lithographic exposure apparatus 102, pre-processing apparatus 106, and post-processing apparatus 108, and include transport apparatus to move the substrates between the various processing modules internal to the substrate track 104. Pre-exposure processes typically performed by apparatus external to the substrate track 106 may include, for example, cleaning, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, and measurement. Pre-exposure processes typically performed by apparatus internal to the substrate track 104 may include, for example, substrate supply, resist coating, measurement, and soft bake. Post-exposure processes typically performed by apparatus internal to the substrate track 104 may include, for example, post-exposure bake (PEB), hard bake, and measurement. Post-exposure processes typically performed by apparatus external to the substrate track 108 may include, for example, cleaning, etching, ion implantation (e.g., doping), metallization, oxidation, chemo-mechanical polishing, and measurement.
To facilitate manufacture of a good substrate, the features and profile of the pattern exposed on the target field of the substrate are replicated as accurately as possible. To this end, one or more attributes of the exposed features on the substrate are typically specified in order to characterize the features and profile of the pattern and establish a benchmark level of quality and/or uniformity. The attributes may include, for example, the gap between features, X and/or Y diameter of holes and/or posts, ellipticity of holes and/or posts, area of feature, feature sidewall angle, width at the top of a feature, width at the middle of a feature, width at the bottom of a feature, and line edge roughness.
There are, however, numerous activities during the lithographic fabrication process that may affect attribute uniformity and/or compromise the quality of the exposed pattern. For example, the very pre- and post-exposure processes that service and treat the substrates along the substrate track, such as the post exposure bake (PEB) processing module, may contribute to variation in attribute uniformity. Such a variation may occur across a target field, across a substrate, and between substrates and ultimately result in loss of yield.